It has been previously suggested in U.S. Pat. No. 5,862,431 to Christensen to measure the level of powdered toner in a toner reservoir of a printer or copier utilizing the electrophotographic, ionographic, or magnetographic technology. One embodiment of the aforesaid Christensen patent has a plurality of fixed piezoelectric film elements mounted in vertically spaced relation in a powdered toner reservoir of a replaceable cartridge.
When the reservoir is full, each piezoelectric film element is immersed in the powdered toner in the toner reservoir. The powdered toner greatly restrains mechanical movement of each of the piezoelectric film elements. Thus, the level of the resulting vibration of each of the piezoelectric film elements is detected by a sensing circuit to determine whether the powdered toner is present in the toner reservoir adjacent the specific piezoelectric film element.
Another embodiment of the aforesaid Christensen patent utilizes a single elongated piezoelectric element. The elongated piezoelectric element has its ends fixed to the top and bottom of a housing forming the toner reservoir. Its resulting vibration varies as the level of the toner decreases.
In either arrangement of the aforesaid Christensen patent, the volume of the toner reservoir in which a stirring paddle can rotate to stir the powdered toner is limited. Accordingly, the possibility exists that the powdered toner may not be stirred sufficiently in all locations in the toner reservoir to produce quality print over a period of time because of the tendency of the powdered toner particles to adhere to each other when not stirred.
U.S. Pat. No. 5,634,169 to Barry et al discloses another arrangement for measuring the level of powdered toner in a toner reservoir of a printer or copier. The aforesaid Barry et al. patent has a stirring paddle on a shaft, which is driven by a driving motor through a torsion spring. As the paddle is rotated through the powdered toner in a reservoir, its shaft lags the rotation of the driving motor. This difference in the angular displacements of the paddle shaft and a driving gear of a gear train driven by the motor indicates the lag of the paddle shaft because of the powdered toner in the reservoir.
The lag number, due to the difference in the amounts of angular displacements of the paddle and the gear of the gear train, decreases as the level of the powdered toner in the reservoir decreases. Three different lag numbers are obtained during each revolution of the paddle shaft by the use of an encoder wheel on the opposite end of the paddle shaft from its connection to the driving motor.
The largest of the three lag numbers indicates the greatest resistance encountered by the paddle in rotating through the powdered toner. The largest lag number indicates which look up table in a ROM is to be employed to provide an indication of the amount of the powdered toner remaining in the toner reservoir.